According to the survey, by the Rasmussen Reports, Mr Obama received 37 per cent support from 510 likely Democratic voters polled on Friday, compared with 27 per cent for the former First Lady and 19 per cent for John Edwards.

In the Republican race, the one-time national favourite, Rudolph Giuliani, trails with just eight per cent, John McCain has extended his lead over Mitt Romney - 31 to 26 per cent - while the anti-war libertarian Ron Paul is third with 14 per cent.